1. Field of the Invention
The invention pertains to sealing arrangements for rotary fluid handling devices, and more specifically, to devices such as turboexpanders and compressors in which a working fluid passes through a rotor while undergoing a pressure change. The rotor typically has a shaft extending longitudinally therefrom and rotating therewith, and both the rotor and shaft are surrounded by a housing which either forms or mounts a set of bearings for supporting the shaft. These bearings are lubricated, usually by a suitable oil.
In general, it is necessary, or at least desirable, to prevent working fluid from entering the bearing area of the apparatus, and conversely, to prevent lubricant from entering the rotor area. One reason for this is that either of these two fluids can interfere with proper functioning of the other. Another reason is that the working fluid is frequently highly explosive, and if it should enter the bearing area, it could eventually leak to atmosphere creating a hazardous situation.
Accordingly, in most such devices, there is a seal between the rotor and the bearing area of the housing, and the lubricant is injected thereinto at a pressure sufficient to cause it to flow axially toward the rotor. This seal may be one of the bearings itself, although it need not be. In many such devices, a second seal, such as a labyrinth seal, is provided about the shaft closely adjacent the rotor to retard the flow of working fluid axially from the rotor area and/or to prevent lubricant from entering the latter area. However, since some leakage of working fluid through the second seal occurs or since a similar or identical working fluid may be injected as a buffer gas, the lubricant and working fluid will come into working contact with each other in a zone between the first and second seals, referred to hereinafter as the "contact zone".
In some systems, a seal gas or buffer gas, which is compatible with, and preferably a component of, the working fluid, is injected into the second seal at a pressure sufficient to cause it to flow in both axial directions, thereby isolating the working fluid from the lubricant. In such systems, some of the seal gas flows into the area of the housing surrounding the rotor and is entrained in the working fluid. Other seal gas flows into the aforementioned zone between the first and second seals and comes into contact with the lubricant.
Thus, in any event, a contact fluid, which, as described, may be working fluid, seal gas, or both, is exposed to the lubricant in the aforementioned contact zone.
2. Description of the Prior Art
For various reasons, it is desirable to collect the contact fluid and lubricant from the contact zone of the apparatus, separate the contact fluid from the lubricant, and recycle either or both of these fluids through the apparatus. Since the contact fluid is much lighter or more volatile than the lubricant, in some instances, at least a major portion of the separation can be achieved by simply directing the contact fluid and lubricant into a vessel maintained at a pressure at which the contact fluid is a gas and the lubricant is a liquid whereby they will separate naturally. Various prior art systems have been devised for this purpose.
However, where the contact fluid is soluble in the lubricant, separation of the two is more difficult, and thus some prior art systems have included means for heating the solution to effect the necessary separation. In these systems, in general, it has been necessary to heat the solution to the boiling point of the lubricant in order to achieve adequate separation. However, such heating is undesirable, since many of the preferred lubricants have boiling points so high that they cannot be heated to the point of vaporization without deterioration of the lubricating properties of the lubricant.